In recent years, electronic consumers products, such as smart phones, tablet computers and video game consoles, often include micro-electromechanical systems sensors (MEMS sensors, e.g., MEMS accelerometer and MEMS gyroscope), and therefore the market for the MEMS sensors has significantly increased. As the technology and products of the MEMS accelerometer has been relatively maturing, the MEMS gyroscope is becoming a promising product in the market. For example, the MEMS gyroscope can be used in the smart phones with the functions of interactive game and navigation.
MEMS sensors such as MEMS gyroscope and comprises a rotary element, a torsion beam, a frame, folded springs and an anchors. The rotary element is connected to the frame via the torsion beam. The frame is connected to the anchor by the folded springs. Moreover, X axis can be defined as the perpendicular direction of extension of the torsion beam, and Y axis can be defined as the parallel direction of extension of the torsion beam. The principle of the MEMS gyroscope is described as follows. When the frame oscillates along the X axis, the rotary element oscillates along the X axis accordingly; when an angular velocity is generated along the Y axis, the rotary element may take the torsion beam as an axis of rotation to rotate repeatedly. At the same time, the capacitance between the rotary element of the MEMS gyroscope and electrode on the substrate is changed, so the angular velocity can be calculated.
As for an ideal design, the resonant frequency of the rotary element and that of the frame need to be identical. It can improve the sensitivity and accuracy of the MEMS gyroscope. However, the stiffness of the torsion beam of the MEMS gyroscope is directly proportional to the width of the torsion beam, but the stiffness of the folded spring is directly proportional to the cube of the width of the folded spring. Thus, when the torsion beam and the folded spring are manufactured with the same variation, the offset of the resonant frequency of the frame is larger than that of the rotary element. As a result, under the circumstances that the torsion beam and the folded spring are manufactured with the same variation, the rotary element and the frame may have resonant frequencies with difference during vibration. Furthermore, the greatest amplitude may not be obtained when the rotary element detects the angular velocity. Therefore, the sensitivity of the MEMS gyroscope are lowered.
In addition, the micro-electromechanical apparatus including a rotatable mass (i.e., rotary element), such as MEMS multi-axes accelerometer, MEMS magnetometer and MEMS micro mirror system, usually comprises a torsion beam which is connected to the rotary element to make the rotary element to rotate. When the dimension of these micro-electromechanical apparatus is miniaturized, the torsion beam is lengthened to make the rotary element rotate at specific frequency. Thus, the dimension of the micro-electromechanical apparatus including the rotary element may not be miniaturized while the torsion beams are used.